30 CFR § 75.804
Underground high-voltage cables.
(a) Underground high-voltage cables used in resistance grounded
systems shall be equipped with metallic shields around each power conductor
with one or more ground conductors having a total cross sectional area of
not less than one-half the power conductor, and with an insulated external
conductor not smaller than No. 8 (A.W.G.) or an insulated internal ground
check conductor not smaller than No. 10 (A.W.G.) for the ground continuity
check circuit.
(b) All such cables shall be adequate for the intended current and
voltage. Splices made in such cables shall provide continuity of all
components.
[38 FR 4976, Feb. 23, 1973]